For the purposes of this description only the shunt application will be described.
The basic principle behind the operation of a shunt regulator apparatus to be used with multiple power sources is controlling the current contribution from one or several sources depending on the load requirement. For that purpose, each power source has a shunt dump device connected thereto, said dump device being responsive to a control signal for dissipating all or a portion of the current generated by the corresponding source. Various techniques have been developped to minimise the power dissipation of the dumps. To date, three types of arrangements are available which allow the voltage or current regulation of a power source with a minimum dissipation of the dump: they all use an error amplifier for comparing the voltage on the supply bus feeding the load with a reference voltage and for producing a signal proportional to the detected deviation.
A first circuit arrangement, called analogue sequential shunt regulator, is illustrated in FIG. 1. The error signal V.sub.E is applied to a plurality of amplifier A.sub.i which are connected such as to work in respective and separate voltage ranges. Each amplifier is connected to compare the error signal V.sub.E with a respective reference level V.sub.i for producing a control signal when the error signal exceeds the reference level. The control signal from the amplifier operates the analogue dump shunt module D.sub.i associated with a distinct power source in order to dissipate a portion of or all the current generated by said source.
In this arrangement each dump shunt module should be capable of dissipating power from zero to the maximum shunt power and then again to zero before the next dump shunt module starts operating. Furthermore, regulators of this type are bulky for large powers to be regulated.
A second arrangement, called digital shunt regulator, is illustrated in FIG. 2. In this arrangement the error signal is applied to an analogue dump module D.sub.o which is arranged to dissipate the energy into an impedance Z.sub.o. The voltage across the latter is compared with an upper reference voltage V.sub.1 and with a lower reference voltage V.sub.2 for producing two control signals which actuate a sequencer SEQ, the one control signal in the forward direction and the other control signal in the reverse direction. The sequencer can comprise a digital up/down counter. From every sequencer stage an output signal is derived for controlling switching means B connected in parallel with a power source. When the current on the bus decreases, the error signal increases as does the output voltage from the dump module D.sub.o. When this output voltage reaches to upper reference level V.sub.1 which is set at amplifier A.sub.1, the latter produces a control signal which enables the sequencer to sequence one stage up thereby operating the switching means for shunting the power source associated with this new sequencer stage and causing the regulated current to decrease.
Depending on the state of the sequencer, one or several power sources are shunted. When the current to be dissipated decreases, the error signal decreases also and when the output voltage from the dump module D.sub.o reaches the lower reference level V.sub.2 set at comparator A.sub.2, the latter produces a control signal which enables the sequencer to sequence one stage down, thereby to drive the switching means OFF for allowing the corresponding power to feed its current contribution into the supply bus.
In this circuit arrangement the dump module should be capable of dissipating a maximum power equal to or greater than individual source's power. Also, any sequencer failure results in a loss in regulation. Furthermore, the sequencer is a relatively complex digital device when large power levels are involved.
The third known circuit arrangement is called multiphase pulse width modulation (PWM) shunt regulator. In this circuit arrangement the switching of the power sources is achieved by pulse width modulation. This type of arrangement is illustrated in FIG. 3. Each of the comparators A.sub.i controls switching means B.sub.i connected in parallel with a power source. One input to the comparators is the error signal V.sub.E, the other input is a saw tooth waveform control signal produced by a generator G. The latter is arranged for producing phased control signals. The outputs from the comparators thus are pulses of equal duration but with a phase displacement of a fraction of a period. The switching means B.sub.i are thereby operated one after the other with a time interval therebetween.
In this arrangement the mode of operation causes current to be sequentially pumped at a given frequency into a supply bus. As the load current requirement increases, then the width of the control pulses decreases and thus overlapping of the currents occurs, which implies that the bus current has developed DC- and AC-components , the AC-component being always equal to the short-circuit current of one source. This AC-component should be filtered by a capacitor.
In this arrangement all the power sources are switching, the implication being that a failure results in the voltage ripple on the supply bus being increased. Furthermore, the control signal generator is a complex apparatus which, in case of failure, causes a loss in regulation.